The present invention relates to a method for hot filling containers and, more particularly, to a hot-filling method and an associated container or closure.
In order to maintain product quality and consumer safety, most foodstuffs are packaged in a hot-fill operation in which the foodstuffs are placed in the containers while hot. During filling, the container subjected to elevated temperatures (i.e., the product temperature, which is typically on the order of 82° C., or higher), sealed, and then cooled.
Hot-filling is commonly used in the bottling of beverages, such as fresh or frozen drinks, fruit juices, isotonic (sports) beverages, etc. These products are typically packaged in PET bottles, which are light, tough, and well suited to the lifestyles of today's consumers.
The design of PET bottles for use in hot-fill operations is not a simple matter. At elevated temperatures, PET softens and loses its shape. The bottles are subjected to hydrostatic pressure exerted on the sidewalls of the container by the weight of the hot liquid, causing the sidewalls to bulge outwardly. During capping, further swelling of the container occurs as the air in head space expands. Finally, as the bottle cools, the volume of the contents, both liquid and air, contracts, causing the bottle sidewalls to collapse inwardly.
To prevent excessive or uncontrolled distortion of the container upon cooling, hot-fill containers are commonly formed with vacuum panels in the middle portion of the sidewalls. As a container is cooled, the vacuum panels move inwardly to accommodate the vacuum formed in the interior of the container.
The need for vacuum panels complicates meeting other packaging requirements, such as providing the mid-section of the bottled with consumer information, promotional graphics, and a grippable profile. Vented container closures incorporating hydrophobic membranes (i.e., membranes that allow air but not liquid to pass therethrough) are known. Their use would relieve the negative internal pressure experienced during container cooling and still seal the container against leakage. However, because such vented caps also permit gaseous fluids to migrate into the heads space of the bottle, both the quality (e.g. the taste profile) and the safety of the contents could potentially be compromised.
Accordingly, it is an object of the present invention to provide a method for hot-filling PET containers that provides for venting during cooling and an air tight seal thereafter.
It is a related object to provide a PET container and/or closure that can be used in the method.